Evaluation of the dynamics of the infection by Rickettsia amblyommii in naturally infected-Amblyomma cajennense ticks

Abstract

The bacterium Rickettsia amblyommii belonging to the spotted fever group was described for the first time in Brazil in 2004, from cajennense Amblyomma ticks collected in the state of Rondônia, Amazon. Since then, this bacterium has been described infecting ticks in different biomes in Brazil and other Latin American countries besides the United States. Currently, the pathogenic role of R. amblyommii in humans remains unknown. However, recent studies have shown serological human infection by R. amblyommii, but without evidence of disease. These results implicate A.cajennense as vector potential A. amblyommii in Brazil, especially in the Amazon region. Thus, this study will seek to directly collected ticks of Rondônia, which will be brought to the laboratory and fed in domestic rabbits. From naturally infected females and females, uninfected A. laboratory colonies will be formed cajennense, which will be used in this study, which aims to: (1) evaluate the vector competence of larvae, nymphs, and adults of A. cajennense in transmitting R. amblyommii to susceptible hosts; (2) assess and quantify the transovarial transmission R. amblyommii in naturally infected ticks A. cajennense; (3) assess and quantify the transestadial transmission R. amblyommii in A.cajennense naturally infected ticks. The first objective will be pursued by clinical evaluation and mostly by serology of infested host larvae, nymphs, and adults of the experimental groups. These results will be compared with tick frequencies found by PCR at each stage of the tick. The second objective will be assessed by PCR eggs and hatched larvae of the experimental groups, as well as by serology and clinical evaluation of hosts infected with larvae coming from females of the experimental groups. The third objective will be assessed by PCR unfed nymphs and adults who change their larvae and engorged nymphs, respectively, after feeding on hosts in the experimental groups, and through clinical and serological evaluation of infested hosts with these nymphs and adults. The quantification of infected nymphs and adults will be performed by PCR, performed individually on each tick not fed. The results of this project will enable a better understanding of the dynamics of R. amblyommii in tick infection in order to infer a possible need for amplifying hosts in the natural history of spotted fever group agents in Brazil.(AU)